This invention relates to a seat adjuster or track assembly for supporting a vehicle seat for selective back and forth adjustment in the passenger compartment of the vehicle.
Typically, the front seat of the vehicle is supported by two adjustable track assemblies, there being one track assembly beneath the seat along each side thereof. Each assembly comprises an upper track secured to the lower side of the seat and supported on a lower track to move back and forth in the passenger compartment. The lower track is anchored to the floor pan of the vehicle. A latch normally holds the upper track against movement relative to the lower track and may be selectively released to permit adjustment of the seat.
Conventionally, the lower track is in the form of an upwardly opening and generally U-shaped channel which is formed with outwardly projecting flanges at its upper end. The upper track is a channel in the shape of an inverted U and includes depending side walls which straddle the lower track. Inwardly projecting flanges are formed on the lower ends of the side walls of the upper track and are disposed in downwardly spaced opposing relation with the flanges of the lower track.
In order to enable the upper track to move along the lower track with relatively low friction, bearing assemblies are interposed between the two tracks. In a conventional track assembly, two bearing assemblies are located between the tracks and are spaced from one another along the tracks. Each bearing assembly comprises a retainer, a cylindrical roller located at the center of the retainer, and spherical balls located at opposite sides of the retainer. With such a bearing assembly, the roller supports the load of the seat and pushes upwardly on the upper track and downwardly on the lower track. The balls are located at the lower corners of the upper track and act against the opposing flanges of the tracks so as to push downwardly on the upper track and upwardly on the lower track. In this way, the balls take up vertical play between the two tracks and prevent the upper track from being loose in the upward direction.
For the most part, bearing assemblies of the foregoing type perform admirably. With the balls of the bearing assembly being located at the lower corners of the upper track, the balls break in quickly, exhibit low wear and do not experience detrimental brinelling. In some cases, however, variations in tolerances of the tracks, the retainers, the rollers and/or the balls cause the rollers to contact the retainers and interfere with smooth operation of the track assembly.
In modern seat adjusters, a seat belt anchor is attached to the upper track, usually by means of a bracket, and serves as an anchor point for the fixed strap of a seat belt. As a result of anchoring the fixed strap of the seat belt to the upper track, the seat belt adjusts back and forth with the seat so as to increase the comfort of the passenger. When a frontal crash occurs, however, the load imposed by the passenger against the seat belt is transmitted to the upper track and tends to move the upper track upwardly and forwardly relative to the lower track. The chances of passenger injury are increased if the upper track is permitted to move during a crash. Thus, the track assembly must be capable of sustaining heavier loads than is the case where the seat belt is anchored to a structure other than the track assembly.